# Probing decoherence in plasmonic waveguides in the quantum regime

## TL;DR

This study experimentally measures decoherence times of single surface plasmon polaritons in metal waveguides, revealing that amplitude damping dominates decoherence, which is crucial for quantum plasmonic device design.

## Contribution

First experimental measurement of decoherence times of single plasmons in waveguides using a Mach-Zehnder setup, highlighting the role of amplitude damping in quantum plasmonics.

## Key findings

- Amplitude damping time T_1 = 1.90e-14 s
- Pure phase damping time T_2^* = 11.19e-14 s
- Total phase damping time T_2 = 2.83e-14 s

## Abstract

We experimentally investigate the decoherence of single surface plasmon polaritons in metal stripe waveguides. In our study we use a Mach-Zehnder configuration previously considered for measuring decoherence in atomic, electronic and photonic systems. By placing waveguides of different length in one arm we are able to measure the amplitude damping time T_1 = 1.90 +/- 0.01 x 10^-14 s, pure phase damping time T_2^* = 11.19 +/- 4.89 x 10^-14 s and total phase damping time T_2 = 2.83 +/- 0.32 x 10^-14 s. We find that decoherence is mainly due to amplitude damping and thus loss arising from inelastic electron and photon scattering plays the most important role in the decoherence of plasmonic waveguides in the quantum regime. However, pure phase damping is not completely negligible. The results will be useful in the design of plasmonic waveguide systems for carrying out phase-sensitive quantum applications, such as quantum sensing. The probing techniques developed may also be applied to other plasmonic nanostructures, such as those used as nanoantennas, as unit cells in metamaterials and as nanotraps for cold atoms.